Saturated fats, unsaturated fats, poly-unsaturated oils, essential fatty acids, trans fats, hydrogenated fats—the world of cooking oils is a confusing one that seems to get more confusing by the minute. And all you want to know is which oil to pour over and your salad, and which oil to fry with. Let’s try and simplify it a bit.
Oils vs fats
They are the same thing. Some tend to be solid, some tend to be liquid, but they are the same thing. So that
bit was easy.
Essential fats
Very healthy oils that our bodies cannot make, and so need to be included in our diet. They are vital for
nerves, for the health of skin and hair and to reduce inflammation. Most commonly found in fish oils and in
plant oils.
Saturated vs unsaturated
This is simply a measure of how reactive the fat is, and so how likely it is to change when you cook it.
Saturated fats are very stable. They tend to be solid at room temperature, like animal fat or coconut oil, and when you heat them they do not change. Unsaturated fats have a more open chemical structure which can change shape when heated, or when reacted with other chemicals.
Poly-unsaturated vs mono-unsaturated
Again, a measure of reactivity. Mono-unsaturated oils are only a little bit unsaturated and so are mostly stable. As such it takes quite a lot of heat to get them to change shape. Polyunsaturated oils are very unsaturated and so are highly reactive. They practically change shape on a sunny day.
Trans fats vs hydrogenated fats
They are the same thing. If you had a degree in chemistry you might argue with that, but in terms of your health they are the same thing. Trans fats are what happens to an unsaturated fat when you heat it up, trans simply meaning change. So if you take a poly-unsaturated fat and heat it a little bit, you end up with a trans fat. If you take a mono-unsaturated fat and heat it a lot you end up with a trans fat. If you take a saturated fat it doesn’t matter how much you heat it, you will never get a trans fat.
Good fats vs bad fats
It used to be that saturated fats were going to clog your arteries and give you a heart attack, while polu-unsaturated fats were going to help you live longer. This is sort of true, although there are some saturated fats that are better than others, but what is more true is that it doesn’t matter how bad saturated fats are, trans fats are worse.
The problem with trans fats is that your body does not recognise them, and so can’t digest them. Neither can anything else – there was a Blue Peter experiment I remember from when I was a child where we put a dish of butter and a dish of margarine, which at the time was all made from trans fats, on a windowsill, and see what happened. While the butter went rancid and mouldy, the margarine sat there, impervious to all bacterial or fungal attack. Never eat anything that does not decompose.
As we are not able to digest trans fats, they just hang around causing problems digesting proper fats in your stomach, and then settling out on blood vessel walls, or in fatty tissue. Trans fats are the main type of fat contributing to heart disease and obesity.
So what do we do?
As we can see, in whatever oils we eat or cook with, the aim is not to make any trans fats. The simple rules are
- Dont’ cook with polyunsaturated oils
- Only medium fry with mono-unsaturated oils
- Use saturated oils for very high temperature cooking
So what should you have in you kitchen?
Sunflower Oil
A polyunsaturated oil. So don’t fry with it. However, it is very good for you in its natural state with lots of vitamin E and healthy essential fats, so makes good salad dressings. Because of their reactive nature poly-unsaturated oils also go off quicker, so don’t keep sunflower oil kicking around for too long.
Olive oil or rapeseed oil
Both mono-unsaturated oils, so ideal for shallow frying. Olive oil is also very popular in dressings because of its taste and so is the more versatile of the two. Rapeseed is slightly better for frying as it can withstand higher temperatures.
Coconut oil
A saturated fat, but one that comes with many health benefits, coconut oil is great for high temperature cooking like stir frying or roasting. It can be bought in its virgin form, or having been heated and cooled to get rid of the fragrance. You don’t really want coconut flavoured roast potatoes.
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Hi, where should we stand on butter (OK, maybe not literally!) especially in respect of cooking with it? And is rice bran oil any better for cooking than sunflower oil? It says that it has a higher smoke point which seems like a good thing, and has very little flavour and is also not expensive (though I’ve not found an organic version yet).
Thanks
Personally I like cooking with butter for the extra flavour, but if you want to cook at high tempereture with it I would use clarified butter or ghee, which is just the fat of the butter with the milk solids removed. This is a good high temperature cooking fat, as like coconut oil it is very saturated and has a high smoke point, but unlike coconut oil it is very fattening, so I would go easy and use it now again as a treat or for a particular dish, rather than use it as your everyday oil.
Al
Interesting article, thanks Al.
Could you comment on the processing of oils? In reading I’ve done recently, I’ve learned that even using sunflower oil in salads is suspect, if it isn’t cold-pressed.
Doesn’t the industrialized processing of seed oils require that they be bleached and deodorized at the end of the process, because the heat applied to them in the processing makes them rancid?
Hi Brian
I would always buy cold pressed oil, as if the oil has been heat treated to get every last drop out of the seed press then you know any poly-unsaturates have already been made into trans fats, and that many of the nutritional benefits will have been lost. This is obviously more important for the vey unsaturated oils that you might be using as a salad oil, such as sunflower. It is also a guarantee that the oil has not been solvent extracted, or had any number of what I am sure are quite unsavoury practices applied to it. And you are right, heat extracting an oil will cause the vitamin E in it to go rancid if it is then stored for long periods on a supermarket shelf, so that must be dealt with somehow. It is for the same reason that they take the wheatgerm out of wheat before making flour, so we end up with nutritionally empty flour that lasts a long time. Great.
I think Chuck Norris may have met his match with Charlie Sheen